Here's some, but probably not all of the reason to oppose the death penalty.
1) Principle - "I don't think the state should execute prisoners under any circumstances."
2) Economics - "The cost of a trial and appeals in a capital case is prohibative. That money could be spent in much better ways."
3) Failable - "Our legal system has proven to be less than perfect. There have been a number of people found guilty of crimes they did not commit. There is no way to reverse an execution."
4) Cruel & Unusual - "Putting someone to death is both cruel and unusual and therefore prohibited by the 8th amendment."
5) Geo-Political - "Most countries do not have the death penalty and look at our practices as being barbaric."
Anyone wanna take these on or bolster these up? Anyone have ones that I've missed?